A large problem with most of the megaliths is that most of the stones have been reset by well-meaning types withoit really understanding the consequences - and not just at Stonehenge either. Some of that occurred in the 20th century but some in much earlier times.
Thom realised that, and that it meant interpretation of the surveys could be somewhat doubtful.
http://articles.adsabs.harvard.edu//...00075.000.html
FYI this prolific fellow:
https://en.wikipedia.org/wiki/Otto_E._Neugebauer
I have a copy of his work, reprinted.